Composition and process for inhibiting corrosion of non-ferrous metal surfaced articles and providing receptive surface for synthetic resin coating compositions

ABSTRACT

Compositions and a process are provided for inhibiting corrosion of non-ferrous metal surfaces and for producing a surface to which synthetic resin coating compositions will adhere so that the resultant coatings have satisfactory impact and bending resistance, together with resistance to creeping corrosion between the metal and the dried resin coating.

United States Patent Miller Aug. 28, 1973 [5 COMPOSITION AND PROCESS FOR3,404,046 111/1968 Russell et al 148/62 X INHIBITING CORROSION 03,380,858 4/1968 Champaneriea et al 148/61 NON FERROUS METAL SURFACE!)3,098,775 7/1963 Thirsk 143/62 3,501,352 3/1970 Shah 148/62 ARTICLES ANDPROVIDING RECEPT IVE SURFACE FOR SYNTHETIC RESIN COATING COMPOSITIONSRussell C. Miller, Chicago, 111.

J. M. Elt zroth & Associates, Inc., Schaumburg, 111.

Filed: Apr. 26, 1971 Appl. No.: 137,682

Inventor:

Assignee:

Field of Search 148/62, 6.21

References Cited UNITED STATES PATENTS 7/1968 Russell et a1 148/62Primary Examiner-Ralph S. Kendall Attorney-Johnston, Root, OKeeffe,Keil, Thompson & Shurtlefi ABSTRACT 4 Claims, No Drawings COMPOSITIONAND PROCESS FOR INI-IIBITING CORROSION OF NON-FERROUS METAL SURFACEDARTICLES AND PROVIDING RECEPTIVE SURFACE FOR SYNTHETIC RESIN COATINGCOMPOSITIONS BACKGROUND Non-ferrous metal surfaced articles, forexample, aluminized and galvanized iron and steel, aluminum,aluminum-zinc alloys, magnesium, and magnesiumaluminum alloys may suffersurface deterioration by corrosion through contact with the atmosphereor moisture, or both. Chemical passivation treatments are widely used toinhibit or suppress such surface corrosion.

One of the passivating treatments employed for this purpose consists intreating the non-ferrous metal surface with an aqueous solution ofchromic acid, or a mixture of chromic acid and dichromate, preferablywith a part of the hexavalent chromium reduced to the trivalent state.

While chromic acid based passivating solutions have been widelyadopted,they have been by no means effective in preventing corrosion under allconditions, particularly in high speed operations and especially wherethe treated surface is further coated with a synthetic resin coatingcomposition which dries to form a synthetic resinous film. The manner inwhich the nonferrous metal surface is pretreated may make the differencebetween satisfactory adherence of the resinous film to the substrate andnon-adherence as well as satisfactory resistance of the coating or filmto impact, bending, and creeping corrosion between the surface of themetal and the resinous film.

It would be desirable, therefore, to provide a process in whichcorrosion of the non-ferrous metal surface is inhibited and wherein thenon-ferrous metal surface is receptive to a synthetic resinous coatingcomposition so that the resultant coated products containing a driedfilm of the resin have satisfactory impact and bending qualities as wellas resistance to creeping corrosion beneath the coating of syntheticresin. It would also be desirable to provide a process in whichnon-ferrous metal surfaced articles such as aluminized; and galvanizedsheets, coils, wires, tubes and rods, can be treated at higher linearspeeds of, say, 100 to 500 feet per minute or even higher so as toproduce a treated article which is corrosion resistant and has a surfacewhich will adhere to synthetic resin coating compositions, therebyproducing coated articles having the physical and chemicalcharacteristics previously mentioned.

OBJECTS One of the objects of the present invention is to provide a newand improved process for making said nonferrous metal surfaced articles,for example, galvanized iron and steel, with surfaces inhibited againstcorrosion and adapted to adhere to synthetic resin coating compositions,thereby producing articles coated with a synthetic resinous film havingsatisfactory impact and bending resistance and resistance to creepingcorrosion between the metal and the resinous coating.

Another object of the invention is to provide a process of the typedescribed in which a non-ferrous metal surfaced article is brought intocontact at a high rate of speed, for example, at a linear speed of atleast 100 feet per minute, with an aqueous solution of a compositionwhich will inhibit corrosion of the surface of said article and at thesame time enhance the receptivity of said surface for synthetic resincoating compositions.

A further object of the invention is to produce new and usefulcompositions for treating non-ferrous metal surfaces which are effectivefor the purposes previously indicated. Other objects will appearhereinafter.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention anon-ferrous surfaced article is treated with an aqueous chromatedepositing solution containing hexavalent chromium and trivalentchromium, together with fluoboric acid and- /or fluosilicic acid insufficient amount to enhance adherency of the resultant surface toorganic film forming polymers which dry to a water resistant coating,with the further proviso that said solution is free from phosphoric acidand phosphates and free from nitric acid in any appreciable amount otherthan that occurring by generation within the chromate depositingsolution.

DETAILED DESCRIPTION OF THE INVENTION The composition of the chromatedepositing solution should be such that it will be effective when anonferrous metal surfaced article is brought into contact with it at alinear speed of at least feet per minute and preferably 100 to 500 feetper minute at a pH of 1.5 to 2.5, to deposit a minimum amount ofchromate expressed as chromium of at least 0.2 mg/sq.ft. Thereafter, theresultant surface can be coated or painted with a composition comprisingan organic film forming polymer which dries to a water resistantcoating. If the coating composition containing the polymer isnonaqueous, the chromium coated non-ferrous metal surface should berinsed with water and dried to an acceptable degree (depending on theparticular organic resin) before the coating composition is applied.Preferably, the final rinse water should be on the acid pH side using avery small amount of the chemical treatment bath itself. The amount usedshould be minimized, using just enough to produce a pH value of 4.5 to6.0 (electrometric) in said final rinse.

It is essential for the baked or primer-baked systems (polyvinylchloride, acrylic, epoxy, melamine, polyester, etc.) to be laid-down" ona neutral or slightly acidic substrate surface, but free of chrome orwater spots or stains, or any powdery or loose surface contamination.

Apparently, fluoboric acid removes oxide films from the surface of themetal without replacing them with water soluble substances which causeinferior adherence of the synthetic resin coating compositions.Fluosilicic acid has a similar action. On the other hand, strong mineralacids such as nitric acid and sulfuric acid in any appreciable amount inthe chromate depositing solution tend to produce water solublesubstances on the surface of the metal which leads to inferior adhesionof synthetic resin coating compositions. This does not occur so readily,however, where radicals such as the sulfate or fluoride radicals arepresent in the form of a metallic salt dispersible in the solution.Boric acid can also be a component of the solution. In addition thesolution can contain reducing agents such as, for example, sodiumsulfite and/or sodium nitrite, which are added for the purpose ofpartially reducing hexavalent chromium to trivalent chromium. Phosphoricacid and phosphates are not used because they are reactive withnon-ferrous metal surfaces to form phosphates which might interfere withchromium deposition on the surface.

. In carrying out the process of the invention the temperature of thechromate depositing solution for use on a non-ferrous metal surfacedarticle is normally within the range of 80 to 210 F. and usually 100 to1 F.

The time of contact between the chromate depositing solution and thenon-ferrous metal surfaced article will normally be within the range ofone second to sixty seconds. However, in operations where high speedcoating is not required the time of contact may be much longer. In thelatter case the pH of the solution can also be somewhat higher, butwould be within the range of 0.8 to 5.0.

The chromate depositing solution can have a solids content within therange from 0.2 gram per liter to 75.0 grams per liter, the remainderbeing water, and the chemical composition should be essentially thefollow- Ingredients Grams per Liter Hexavalent chromium (expressed asCR) 0.05-50.0 Trivalent chromium (expressed as Cr) 0.033.0 Fluoride orbifluoride (expressed as F) 0.03-30 Borate (expressed as B, 0,) 0.0l3.0Fluoborate (expressed as BF 0.03-10.0 Sulfate (expressed as S0.) 0.0I3.0Magnesium (expressed as Mg) 0.01-3.0 Aluminum (expressed as Al) 0.0l3.0Iron (expressed as Fe) 0.01-0.05 Nickel (expressed as Ni) 0.0l-0.05Optional:

Acetate (if increased wetting rate is desired) 0.0l0.l Acid stablesurfactant (for increased wetting) 001-01 In addition where the chromatedepositing solution does not initially contain trivalent chromium,sodium nitrite, sodium sulfite, or other reducing agents can be added.The quantity of sodium nitrite and the quantity of sodium sulfite wouldusually be within the range of 0.05 to 0.2 grams per liter.

.The invention will be further illustrated but is not limited by thefollowing examples in which the quantities are stated in parts by weightunless otherwise indicated.

EXAMPLE I A chromate depositing solution was prepared having thefollowing composition:

Ingredients Grams per Liter Na cr, O 2 H, O 6.75 CrO, 1.36 NaF 1.36 H,B0, 1.16 NaHSO, 0.89 Na, SO, 0.2 NaNO, 0.2 MgSO. 0.67 HBF. 50%) 2.73M80; trace FeSO trace This composition makes up to a gram per literchromium depositing solution.

Clean strips of hot-dip galvanized steel were immersed in the abovecomposition at a temperature of 125 F. and agitated manually for aperiod of 3 to 5 seconds after the pH had been adjusted to a value of2.0 by adding NaOH.

The resultant strips were then rinsed with cold water, rinsed with hotwater, dried, and aged for 72 hours at room temperature after which theywere painted with an acrylic resin paint. The resultant product showedexcellent paint adherence with resistance to creeping corrosion beneaththe paint film.

EXAMPLE II A chromate depositing solution was prepared having thefollowing composition:

Ingredients Grams per Liter K2 CT: 1 5.55 CrO, 2.22 NaF 1.15 H, B0, 2.00NaHSO 0.90 Na, so, 0.2 NaNO, 0.2 4) a 0.70 HBF. (50%) 2.50 M50, traceFeSO trace This composition makes up to approximately a 15 gram perliter chromium depositing solution.

The pH was adjusted to 3.0 by adding NaOH and the temperature was raisedto F.

Clean strips of hot dip galvanized steel were immersed in the resultantsolution and agitated manually for a period of 3 to 5 seconds.

The resultant strips were then rinsed with cold water, rinsed with hotwater, dried, and aged for 72 hours at room temperature after which theywere painted with an acrylic resin paint. The product showed excellentpaint adherence with resistance to creeping corrosion between the paintfilm.

EXAMPLE III A chromate depositing solution was prepared having thefollowing composition:

Ingredients Grams per Liter Na, Cr, 0 2 H, O 2.88 CrO, 2.88 NH F'HF 1.00H, B0, 0.80 NaHSO 0.66 Na, SO, 0.1 NaNO, 0.1 MgSO, 0.50 HBF (50%) 1.66M80. trace FeSO. trace This composition makes up to approximately a 10gram per liter chromate depositing solution.

The pH value of the solution was raised to 3.5 by adding NaOH and thetemperature was raised to F.

Hot dip galvanized steel was immersed in this solution for 3 to 5seconds and the resultant product thereafter rinsed, dried, agedandpainted as described in Example I with very satisfactory results.

EXAMPLE IV A chromate-depositing solution was prepared having thefollowing composition:

Ingredients Grams per Liter Na, Cr, 0, 2 H, O 1.66 CrO, 0.33 NaF 0.33 H,B0; 0.33 NaI-ISO, 0.10 Na, SO, 0.05 NaNO, 0.05 MgSO 0.10 HBF. (50%) 0.66N' O trace FeSO trace .This composition makes up to approximately a 3.5gram per liter solution.

The pH value of the solution was adjusted to 2.0 by adding NaOl-l. Thetemperature of the bath was raised to 175 F. and clean aluminum stripswere immersed therein for 5 to seconds. The resultant aluminum stripswere all cold rinsed and warm rinsed with water. Thereafter they weredried, painted with an acrylic resin paint, baked and aged.

EXAMPLE V The procedure was the same as in Example 1 except that the pHof the solution was adjusted to 1.5 by adding HBF, and the temperaturewas raised to 150 F. Clean strips of mill-run aluminum were immersed inthe solution with agitation for a period of 5-l0 seconds. The resultantaluminum strips were then rinsed with cold water, followed by a warmwater rinse and dried. They were thereafter painted with an acrylicresin paint, baked and aged.

EXAMPLE VI EXAMPLE VII The procedure was the same as in Example lIIexcept that the pH of the solution was adjusted to 2.0, and cleanaluminum strips were immersed in the solution at a temperature of 165 F.for a period of 5-10 seconds with agitation. The resultant strips weresubsequently recovered, rinsed, dried and painted as described inExample VI.

EXAMPLE VIII The chromate depositing solution was made up as describedin Example IV. The pH value was adjusted to 1.5 by adding HBF Thetemperature of the bath was adjusted to 150 F. and clean strips of hotdip galvanized steel were immersed therein and agitated manually for aperiod of 3 to 5 seconds. Thereafter the resultant strips were rinsed,dried, aged and painted as described in Example I.

The procedures described in Examples IV to VII were also carried outusing clean strips of aluminum alloy 3003 and 2024.

The sheet panels produced as described in the examples were coated withprimer coats and also with primer coats and finish coats. Various primercoats were used, for example, Lily Varnish Primer 465 and 11 PL Primer12870. Various finish coats were used, for example, Acrylic JT 411-3,Duracron Super 610 and Duracron Super 810. The resultant products weresubjected to corrosion resistance tests (ASTM-B-l 17- 64). They werealso subjected to pull-away tests with pressure sensitive adhesive tape(3-M transparent No. 600). They were subjected to various bending testsincluding pull-away tests at the bend. In addition they were subjectedto hardness tests and impact tests. The impact tests were made on aGardner impact tester at pressures of 130-160 pounds per square inch'.The products satisfactorily passed these tests.

While acrylic resin coating compositions are especially useful, otherorganic film forming polymers can be employed, for example, polyvinylchloride, epoxy resins, mixed epoxy-acrylic resins, polyester resins andpolyurethane resins.

In the practice of the invention as will be seen from the foregoingexamples, the chromate depositing solution is normally made up first asa solution containing hexavalent chromium compounds, namely, dichromatesand chromic acid, together with other additives. In general, thechemical composition of the initial solutions is essentially as follows:

Ingredients Grams per Liter Dichromates (e.g., Na, Cr, 0, 2

or K, Cr, 0,) 1.66-6.75 Chromic acid 0.33-2.88 Sodium or ammoniumfluoride or bifluoride 0.33-1.36 Boric acid 0.33-2.00 Sodium acidsulfate 0.10-0.90 Aluminum sulfate 0-0.70 Magnesium sulfate 0-0.70Fluoboric acid (50%) 0.66-2.75 Nickel sulfate (NiSO trace Iron Sulfate(FeSO trace To this solution the reducing agents'are added to generatetrivalent chromium in situ. As indicated by the examples, it ispreferable to use sodium nitrite and sodium sulfite as reducing agentsand the amount used is approximately one percent of each, based on thetotal weight of all of the materials contained in the concen tratedaqueous solution. Other reducing agents can be employed such as, forexample, zinc dust, cadmium dust, potassium sulfite, sodium bisulfite,sodium hydrosulfite, and sodium thiosulfate.

Nitrates can also be used in the foregoing compositions and theirpresence in low concentrations give better coatings and productexcellent undercoated sur faces for application of organic coatings.

It will be understood that while the operating pH for high speedproduction is usually within the range of 1.5 to 2.5, the pH can varywithin the broader range of 0.8 to 5.0 under other operating conditionsdepending upon time of contact of liquid and substrate, temperature,concentration, preliminary preparation, and method of application. It isimportant that the nonferrous metal substrate be clean and that alloxide be removed therefrom before treatment with the chromium depositingsolution. The time of treatment can vary from one second to five minutesand the solids concentration of the treating chromium depositingsolution from 0.5 ounce per gallon to 12 ounces per gallon. Thenon-ferrous metal surface can be immersed in the chromium depositingsolution with or without agitation or the chromium deposition solutioncan be applied by spraying or by a combination of spraying andimmersion.

The presence of trivalent chromium is particularly important where thenon-ferrous metal surface is composed of aluminum or aluminum alloymaterials. In hot dip galvanized lines hexavalent chromium is producedby the action of the acid on zinc and at least a minimum amount ofreducing agent should always be present to insure the development oftrivalent chromium.

While the invention has been described particularly with respect to zincand aluminum surfaces, especially aluminum, aluminum alloys andaluminized and galvanized iron and steel, it is also applicable to othernonferrous metal surfaces including magnesium, magnesium-aluminumalloys, copper and copper alloys, and copper-clad phenolic sheets.

The invention makes it possible to provide nonferrous metal surfacedarticles which are inhibited against corrosion and adapted to adhere tosynthetic resin coating compositions thereby producing articles coatedwith a synthetic resinous film having satisfactory impact and bendingresistance and resistance to creeping corrosion between the metal andthe resinous coating.

The invention is hereby claimed as follows:

1. A chromate deposition composition having a solids content within therange from 0.2 gram per liter to 75.0 grams per liter, the remainderbeing water, and consisting essentially of the following:

Ingredients Grams per Liter Hexavalent chromium (expressed as Cr)0.05-50.0 Trivalent chromium (expressed as Cr) 0.03-3.0 Fluoride orbifluoride (expressed as F) 0.03-3.0 Borate (expressed as B 0,) 001-30Fluoborate (expressed as BF 0.03-l0.0 Sulfate (expressed as S 0.0l3.0Magnesium (expressed as Mg) 0.0l-3.0 Aluminum (expressed as Al) 0101-lron (expressed as Fe) 0.01-0.05

Nickel (expressed as Ni) Acetate (as acetate radical) 2. A chromatedepositing composition consisting essentially of an aqueous solution ofthe following:

3. A composition as claimed in claim 2 containing a sufficient amount ofa reducing agent to convert a part of the hexavalent chromium totrivalent chromium.

4. A composition as claimed in claim 3 in which the reducing agentconsists essentially of sodium sulfite and sodium nitrite each inproportions of 0.05 to 0.2 gram per liter.

2. A chromate depositing composition consisting essentially of anaqueous solution of the following: Ingredients Grams per LiterDichromates 1.66-6.75 Chromic acid 0.33-2.88 Sodium or ammonium fluorideor bifluoride 0.33-1.36 Boric acid 0.33-2.00 Sodium acid sulfate0.10-0.90 Aluminum sulfate 0-0.70 Magnesium sulfate 0-0.70 Fluoboricacid (50%) 0.66-2.75 Nickel sulfate (NiSO4) trace Iron sulfate (FeSO4)trace
 3. A composition as claimed in claim 2 containing a sufficientamount of a reducing agent to convert a part of the hexavalent chromiumto trivalent chromium.
 4. A composition as claimed in claim 3 in whichthe reducing agent consists essentially of sodium sulfite and sodiumnitrite each in proportions of 0.05 to 0.2 gram per liter.